This descriptive observational study was carried out to determine the frequency of causes behind Abnormal Uterine Bleeding (AUB) amongst patients of reproductive age presenting to gynaecology OPD from January to June 2018 at the Combined Military Hospital Kharian, a tertiary care hospital. All women presenting with complaints of AUB were enrolled for the study, except for those who were pregnant, adolescent and postmenopausal. Detailed history, physical examination and relevant investigations were done and patients were categorised according to FIGO PALM-COEIN classification system and placed in nine main categories. A total of 238 patients were enrolled and the incidence of AUB among them was found to be 11% according to PALM-COEIN classification system. The frequency and percentage of all etiologies was calculated. Frequency of structural causes was Polyp 10 (6.7%), Adenomyosis 35 (23.5%), Leiomyomata 80 (53.7) and Malignancy 24 (16.1%). Nonstructural causes were Coagulation Disorders 5 (5.6%), Ovulatory 56 (37.6%), Endometrial Dysfunction 3 (3.4%), Iatrogenic 14 (15.7%) and Not-yet-classified 11 (12.4%). Development of a universally accepted classification system is a step towards facilitating clinicians, patients and researchers to communicate with each other and make objective management plans.